View full lesson: http://ed.ted.com/lessons/how-memories-form-and-how-we-lose-them-catharine-young

Think back to a really vivid memory. Got it? Now try to remember what you had for lunch three weeks ago. That second memory probably isn’t as strong—but why not? Why do we remember some things, and not others? And why do memories eventually fade? Catharine Young gives the basics on memory and memory loss.

Lesson by Catharine Young, animation by Patrick Smith.